High-power and fundamental-mode oscillating flared SBA lasers

Shigihara et al. (see ibid., vol.24, no.18, p.1182-3, 1988) have reported on a tapered-waveguide diode laser that maintains a fundamental mode as the stripe width increases from 1.6 to 5.4 mu m. Three comments are made: (i) the far-field beam pattern from the device front facet (i.e. the wide end of the taper) is the Fourier transform of a (raised)-cosine-shaped source; (ii) the doubling in power capability due to the taper can be simply explained by considering Gaussian- and cosine-shaped sources at the narrow and wide ends of the taper, respectively; and (iii) if one assumes a Gaussian-shaped source at the taper wide end, as Welch et al. have done, the near-field spot size is underestimated by as much as 28%.